You say you hear distortion when playing very low notes - those are small speakers and can only take so much. Reverse the speaker position and see if the other one does the same thing. Also, is it only on one recording or does it happen a lot? Sometimes a bass note on a given recording just causes a speaker cabinet to react.
Assuming you determine it's broken, I would contact Fidelis, the Harbeth importer, and ask where you can have the speaker repaired. Fortunately, you don't have the M40s, which are a bit harder to ship. Good luck.
Assuming you determine it's broken, I would contact Fidelis, the Harbeth importer, and ask where you can have the speaker repaired. Fortunately, you don't have the M40s, which are a bit harder to ship. Good luck.